This invention relates to a process for the production of anthraquinone-1-sulphonic acid by sulphonating anthraquinone in the presence of a palladium catalyst, and particularly to a process characterized in that the palladium catalyst is treated with nitric acid or other acids containing nitric acid.
Processes for the production of anthraquinone sulphonic acids are known in the art. German Pat. No. 149,801 discloses a process in which anthraquinone is sulphonated in SO3 containing sulphuric acid in the presence of mercury, mercury salts or thallium salts. However, the sulphonation process according to the above patent is not selective. In U.S. Pat. No. 3,763,191, a process for the production of anthraquinone-.alpha.-sulphonic acids is suggested, especially anthraquinone-1-sulphonic acid by the sulphonation of anthraquinones in the presence of catalysts in solvents, the catalysts being metals of the 1st or 8th subsidiary group of the periodic system or compounds containing such metals. This process provides a high degree of selectivity for anthraquinone-1-sulphonic acid.